1. Field of the Invention
This invention is related to field of statistical quality control and more specifically related to a method of determining an equivalency index of products, processes and services.
2. Description of the Related Art
Every product, process or service possesses a number of parameters that jointly describe what the user thinks of as quality. These parameters are often called quality characteristics. Quality characteristics may be physical such as length, weight, voltage, and viscosity, or sensory such as taste, appearance, color, and ease of use, or time orientation such as reliability, and durability.
In the past, the buyers had to carry the burden of examining, judging, and testing products or services for themselves. Competition in the market place has shifted the burden to the producers. The producers not only must screen out the non-conforming products before they reach the customers, they must continuously monitor their manufacturing processes for continuous quality improvement in order to compete.
To aid such endeavor, statistical tools have been developed. Today, it is common for the producers of automobile, computer, clothing, and its field service, and providers of services such as generation and distribution of electrical energy, Internet services, telephone services, public transportation, banking, health, and accounting to adopt statistical quality control tools in their business and manufacturing operation. Such tools have become indispensable in their endeavor to compete for market share.
Among the tools that are prevalent among the practitioners of statistical quality control are the control chart, the Pareto diagram, the scatter plot, the histogram, the experimental design, and the acceptance sampling.
One common character of these tools is that they are most effective when used to correlate between characteristic quality parameters of a product or a service, and the input or process parameters that can affect the quality parameters. Practitioners use these tools to compare the variation of the quality parameters to the predetermined limits and to distinguish between common and special causes so as to understand and analyze the variation in the quality of a product or a service. Once the causes are identified, the information enables the practitioner to make necessary modification in order to control the effect and reduce the variation. These tools, however, have a common shortcoming.
In today""s business environment, producers may be manufacturing their goods in many production sites, often in distant parts of the world. Service providers may be operating in many diverse geographical locations. Yet, the goods and service must be controlled to the same quality standard. For example, a customer will expect the same quality of food and service from a restaurant in Tokyo, Japan as what he receives from a restaurant in Guadalajara, Mexico if the restaurants bear the same name. A micro-controller chip maker in Taiwan, for example, who tries to qualify as a supplier to a German customer must demonstrate that its chips meet the customer""s specification and are equal, statistically speaking, to the parts the customer currently uses. The traditional statistical quality control methods and tools are less helpful for such purposes. When the issue concerns the degree of equivalency among a multiplicity of products, processes, and services, it is difficult, with such tools, to reach an unambiguous conclusion readily and to express the conclusion in a concise numerical format.
It is the object of this invention to provide a method with which a person of ordinary skill in the area of statistical quality control can determine whether a product, process, or service is statistically equivalent to another of known quality.
It is also the object of this invention to provide a method with which a person of ordinary skill in the area of statistical quality control can determine whether a product, process, or service is statistically equivalent to a required standard.
It is also the object of this invention to provide a method with which a person of ordinary skill in the area of statistical quality control can determine whether a multiplicity of products, processes, or services are statistically equivalent to one another and of a desired quality.
Examples of such occasion are abundant: an owner or operator of a plant may need to judge the quality of a potential electricity supplier in terms of fluctuation of the supply voltage over time and compare that to the current supplier, an electronic system maker may need to judge the quality equivalency of the printed circuit board from a new vendors in terms of the thickness variation of the board in view of his production equipment specifications, other examples are the fill volume of soft drink beverage from various bottling machines, the net weight of a dry leach product from multiple production lines, the tensile strength of alternative new alloy materials for an automotive engine part, the time to failure of an electronic component from different vendors, or the results of many quality-control technicians measuring the surface finish of a metal parts.